Video On Demand (VOD) is becoming a service which cable operators now consider to be a mandatory service as much as subscription and impulse pay-per-view (IPPV). But, VOD is different from broadcast services in that content is statically stored on VOD servers (often at the cable hubs), and is delivered to a specific subscriber upon receipt of a specific request by that subscriber.
VOD servers are often located at cable hub facilities. Hubs are located out in the local neighborhoods and serve a subset of perhaps about 80,000 subscribers. By locating the VOD system at the hub level, use of bandwidth is more efficient since customers in different hubs can use the same spectrum. As a point of contrast, subscription and IPPV content is generally scrambled at a Master Headend and delivered to the hubs for distribution.
There are currently two major VOD service providers in the cable industry. In one, content is stored pre-encrypted on hard drives in the VOD server. The keys used to encrypt the content do not change from month-to-month, however, the entitlement control messages (ECMs) used to derive those keys to enable the conditional access (CA) system are updated every month. In the second VOD system, content is stored in-the-clear on hard drives in the VOD server. The content is encrypted real-time with slow changing keys (lasting 20 minutes or more). For other systems, the VOD content is sent in-the-clear to subscribers. Storage has been typically in-the-clear or encrypted using a simple “storage key”.
The frequency and program identifiers (PIDs) used for a VOD session are privately signaled through encrypted transactions, so that someone trying to eavesdrop on the VOD communication cannot receive the tuning information for the program even if the content is sent in-the-clear. In some systems, the content is scrambled as an IPPV program. The program is therefore “purchased” as in a broadcast IPPV program. If an eavesdropper could locate the VOD channel, he or she would still need to pay for the movie as the legitimate customer.
In addition to the security provided by encryption, encryption of PIDs and frequencies and other measures, VOD security also relies on the fact that both the content and viewing times are under control of a legitimate purchasing party. That party can pause the program for a half an hour or all day. The content can be “rewound” or started over from scratch. These factors all contribute to providing protection against pirating of the content.
For all of the differences between VOD programming and conventional programming for cable and satellite programming, there remains a significant problem when a cable or satellite operator wishes to utilize decoder equipment (e.g., television set top boxes (STBs)) from multiple vendors. As with conventional cable television, each vendor generally uses its own conditional access (CA) encryption system. If a multiple service operator (MSO) chooses to utilize mulitple STBs in a system, it must somehow accommodate multiple CA systems. This problem has been discussed extensively in the above-referenced patent applications. Since VOD content storage is limited, duplicating content so that it may be available to both legacy and non-legacy CAs may not be a practical (because of a lack of rack space), or economical (storage costs money).